Expression and purification of ApxN, P97C, and Ap97 recombinant proteins. A. Coomassie blue-stained SDS-PAGE gel showing ApxN, P97C, and Ap97 purified from E. coli BL21 using His-tag affinity chromatography. The molecular masses of ApxN (lane 1), P97C (lane 2), and Ap97 (lane 3) were approximately 15, 45, and 60 kDa, respectively, which were equivalent to the expected values. B, C, and D. Western blot analysis of ApxN, P97C, and Ap97 using antisera from mice immunized with Ap97 (B), ApxN (C), or P97C (D) vaccines. The mouse antisera were obtained 3 weeks after the last immunization (Day 63).